When you play two notes in a row, your brain does not initially recognize “C to E” or “G to B”, but distance. This distance is an interval, and it is the building block of melody. Rather than memorizing silly syllables, try listening for whether the second note feels close, somewhat distant, or a long jump. At a piano or keyboard, play C and D together for a beat or two, then play C and G together for a beat or two. The shorter distance feels more like a conversation, whereas the greater distance feels more like a swiveling of the head.
A fifteen minute practice might be limited to just a single starting point. Let’s say middle C. Try jumping up to another note, and then come back to C. Before you look at the distance on the keyboard, call it small, medium, or large. When you say it out loud, you commit to the judgment, rather than just passively listening. After a few minutes, your ear starts to classify them for you. Much better than using song associations, because we’re making a direct association between what we’re hearing, and the classification, rather than relying on a memory trick.
Incorrect approach: You play the two notes once, and try to make a decision. A common error among people just starting out is to play the two notes, make a wild guess, and then move on even though they’re not really sure. Ear training is a process of repetition: If you’re having trouble hearing two notes, play them 5 or 6 times in a row, and if necessary, play them a little softer or louder, or a little faster or slower. Often, your brain will need to hear the two notes a few times in order to really “catch” the interval. A second useful thing you can do is sing the first note before playing the second. By singing, you are fixing the first note in your mind, and it will be easier to judge the interval when you play the second note.
It is frustrating when intervals appear to be the same, particularly when they are of the same “color.” Rather than trying to sort out every possible distance, concentrate on identifying very small steps for one day, without trying to discriminate between larger ones. When that division becomes clear, add another one. This process of discrimination is similar to the way that you would originally have developed your sense of pitch, and it avoids the confusion and discouragement that leads so many students to give up on ear training too soon.
With further sensitivity, you can begin to perceive the shape of melodies even before you determine the specific notes. Perhaps a melody moves up tentatively and then makes a big jump, generating excitement. Practice further by creating small two-note phrases and attempting to repeat them without looking. The goal here is not so much to determine which pitches they are as to feel how far apart they are. Eventually, the intervals cease to be merely names and acquire the sense of specific distances, so you begin to have an internal yardstick for any melody.